The present invention relates to a gear change for a vehicle and in particular, but not exclusively, for an industrial vehicle.
As is known, one of the most important requirements at present in the design of vehicles in general is to reduce the weight of components. For this purpose attempts have been made, where this is possible and compatible with mechanical stresses and thermal operating conditions, to produce components traditionally made from steel or cast iron from light alloy or synthetic materials.
The overall weight of gear changes for automobile vehicles can in particular be substantially reduced by producing the external box from aluminium alloy rather than cast iron.
This entails designing the gear change components so as to reduce the chain reactions on the box so that the resulting stresses are admissible from the point of view of the mechanical strength of the material.
The production of the box from aluminum alloy entails a drawback associated with its coefficient of thermal expansion which differs from that of the steel and iron materials in general from which the movable transmission components (shafts, toothed wheels) necessarily have to be made.
In particular, since the coefficient of thermal expansion of aluminum alloys is much greater than that of iron materials, increasingly substantial axial play is generated between the shafts of the gear change and the box as the temperature increases.
This play, of some millimeters at operating temperatures, makes the actual axial position of the gears and coupling sleeves uncertain and may therefore compromise the regularity and reliability of the coupling movements.